[clang] [flang] [flang][Driver] Better error message when multiple actions are specified (PR #165575)

[Tarun Prabhu via cfe-commits]

================
@@ -312,6 +312,8 @@ def warn_drv_yc_multiple_inputs_clang_cl : Warning<
 def warn_drv_potentially_misspelled_joined_argument : Warning<
   "joined argument treated as '%0'; did you mean '%1'?">, InGroup<UnknownArgument>;
 
+def err_drv_too_many_actions: Error<
+    "only one action option is allowed. Got '%0'">;
----------------
tarunprabhu wrote:

It is not part of the substitution syntax. Most of the other diagnostic messages are written this way, but they only ever print a single option. You're right, it does make more sense to remove them from here. 

Apologies for not addressing your original issue sooner.

https://github.com/llvm/llvm-project/pull/165575